1. Field of the Invention
The present invention relates to the refining of sulfur-bearing materials containing quantities of nickel and copper values, such as nickel-copper-sulfur concentrates and in particular nickel-copper matte, by hydrometallurgical treatment.
2. Description of the Prior Art
Hydrometallurgical processes for refining copper-nickel-sulfur concentrates and mattes are known in which the desired metal values are dissolved in one or more leaching stages, and copper is eventually recovered electrolytically. These processes generally have one or more disadvantages, such as the production of by-products which contain sufficient amounts of copper and/or nickel that further treatment of the by-products is necessary for recovery of the nonferrous metal values. Another disadvantage is that these processes consume energy in amounts that, though relatively significant, have heretofore been considered necessary.
For instance, U.S. Pat. No. 814,049 discloses a process in which copper-nickel matte having a copper:nickel ratio of, for instance, 1:1 is leached in sulfuric acid to form a nickel sulfate solution, hydrogen sulfide gas, and a leach residue comprising sulfides of copper and nickel. The residue is then roasted to form a mixture of copper and nickel oxides, and the oxide mixture is leached with sulfuric acid to form a solution containing, for instance, 9% copper sulfate and 1% nickel sulfate. This solution is then subjected to electrowinning to recover a cathodic copper deposit, and the electrolyte is recycled to the oxide leaching stage. The electrolyte is periodically withdrawn, subjected to further electrowinning to lower the copper content to about 0.4%, and then recycled to the matte leaching stage where the residual copper reacts with hydrogen sulfide and precipitates as copper sulfide. This process presents the drawback that leaching the copper-nickel oxide leaves substantial amounts of nickel in the leach residue which would therefore require additional treatment not described in the patent to recover the nickel. In addition, the cathodic copper deposit produced in the electrowinning step in which the copper content of the electrolyte is lowered to 0.4% copper would be of poor quality and might have to be refined further to separate the copper and nickel into acceptably pure products.
U.S. Pat. No. 882,075 discloses a process for treating copper-nickel matte in which all of the matte is initially roasted, and the entire quantity of roasted material is smelted to produce a copper-nickel alloy. A portion of the alloy is cast into anodes, and the remaining portion is dissolved in sulfuric acid to form a copper sulfate-nickel sulfate solution. The copper-nickel anodes are electrorefined in the copper sulfate-nickel sulfate solution to form a cathodic copper deposit and a nickel-enriched electrolyte. This process has the drawback that it cannot produce both a high-quality cathodic copper deposit and a nickel sulfate solution substantially purified of copper sulfate, without further treatment of either the deposit or the solution; continuing electrolysis to the point that copper is substantially removed from solution produces a cathodic deposit of unacceptable quality.
U.S. Pat. No. 1,844,937 discloses another process in which all the copper-nickel matte fed to the process is initially roasted. The roasted material is divided into two portions. One portion is smelted to produce copper-nickel anodes, and the other portion is leached with sulfuric acid to form a copper sulfate solution and a copper-nickel residue. The copper-nickel anodes are electrorefined in the copper sulfate solution to produce a cathodic copper product and a nickel-enriched electrolyte. The copper-nickel residue is smelted separately to form anodes which are electrolyzed in the nickel-enriched electrolyte in order to further enrich the electrolyte in nickel and to deplete its copper content to about 5 gpl. This process has the drawback that the cathodic copper deposit produced in the latter electrolysis includes a substantial portion of low-grade copper which must be subjected to further refining in order to provide copper of commercially acceptable purity.